This invention pertains to laminated sheet materials used for packaging. Such sheet materials are commonly known for their use in making bags, pouches, and tubes. The sheet materials of the invention can be used for making any of these types of packages. This particular description will be addressed primarily to the discussion of the sheet materials as they relate to packaging products in lap seamed tubes.
Laminated sheet materials of the variety disclosed herein, and especially those containing a layer of metal foil, have been used for packaging such materials as toothpaste, foods, and certain chemical compounds. There remain certain products which have not heretofore been packaged in multiple layer sheet materials of the type disclosed in the invention because of the package's susceptibility to being chemically attacked by the contained product. Particularly troublesome, and addressing now the problem addressed by the inventors herein, are those compounds which use especially volatile, and chemically active, materials such as methyl salicylate.
Conventional sheet materials of the type disclosed in this invention contain a barrier layer of aluminum foil, and protective, covering, sealing, bonding, and the like layers of polymeric materials on both sides of the aluminum foil. It has been found unsatisfactory to package products containing methyl salicylate in known sheet materials of this type because methyl salicylate penetrates through the intervening polymeric layers and attacks the interfacial adhesion on the product side of the metal foil layer. The attack on the metal foil interfacial adhesion is effective to cause delamination of the sheet material, and subsequent failure of the package.
There are a number of advantages to the laminated type of sheet material of the invention over the otherwise conventionally used packages of metal foil. The conventional tubes of metal foil, which are used for packaging these hard-to-hold products, have a number of disadantages. Among the disadvantages are the thickness of the metal foil which is used, and its associated tendency to crack upon repeated flexing. Metal foil tubes are also more expensive. While such disadvantages have been known for quite some time, there has not, in the past, been a satisfactory substitute material for use in packaging the materials addressed by the inventions herein.
Thus it would be highly desirable to find a functionally acceptable material which can be used to package materials which attack the more conventional multiple layer sheet materials which are used in packages of this type.
It is an object of this invention to provide multiple layer sheet materials capable of holding such a volatile material as methyl salicylate in combination with a metal foil which provides a high barrier to the transmission of product components through the package wall.
It is another object of the invention to provide a multiple layer sheet material which is capable of holding certain volatile materials, without delaminating, over the typical life of the product.
It is still another object of the invention to provide a multiple layer sheet material which is capable of holding products containing methyl salicylate and similar materials for the expected shelf life of the product without significant loss of any of the volatile components, and the resulting change in the product composition.